Tricuspid valve disease has generally been dealt with as an isolated valvular lesion. However, tricuspid regurgitation generally occurs in association with mitral valve disease. Tricuspid regurgitation results from either organic disease of the valve or more commonly from the effects of mitral valve disease of the right ventricle and the tricuspid valve annulus. To determine the incidence and severity of tricuspid disease in association with initial mitral valve disease we studied a group of 47 patients with pure, chronic mitral regurgitation with and without tricuspid valve regurgitation. Preoperative features and operative findings were statistically compared. The 22 patients without and the 25 patients with tricuspid regurgitation were similar except for the duration of symptoms. The latter group had a six year or more duration whereas those without tricuspid regurgitation came to surgical palliation much sooner. Palliation of symptoms was of longer duration in those without tricuspid regurgitation. These data suggest that postponement of mitral valve surgery after the onset of significant symptoms have occurred results in poor prognosis.